The Oklahoma City area appeared to be the hardest hit, with as much as eight inches of rain reported within hours, according to the National Weather Service.

At least 13 people were injured when a tornado hit a mobile home park, said Susie Patterson of the Emergency Medical Services Authority in Oklahoma City

The city's main threat Wednesday night were flashfloods as residents reported washed-out roads.

\"There's debris just everywhere, and there's a lot of water on the roadways,\" Capt. Paul Timmons of the Oklahoma Highway Patrol told CNN's \"Erin Burnett OutFront.\"

No flights out

Low visibility made it difficult to reach some affected areas, Timmons said.

The National Weather Service declared a flash flood emergency -- the first in Oklahoma City's history. The city's main airport canceled all flights for the rest of the night Wednesday and evacuated passengers and employees to a pedestrian tunnel.

\"There will be no more flights tonight at WRWA,\" the Will Rogers World Airport tweeted.

Damaging winds, lightning and tornadoes also affected the area, Oklahoma City officials said in a situational update.

The storms are part of a larger system going through Kansas, Oklahoma and Texas, CNN meteorologist Jennifer Gray said.

Hospital on generator power

The Norman Regional Hospital in Oklahoma City had some minor damage and is on generator power but is fully operational, health officials said.

Norman hotel also sustained some damage.

In Bridge Creek, Oklahoma, about 30 miles southwest of Oklahoma City, forecasters warned residents to take cover as the Weather Service issued a tornado emergency and said a large, destructive twister was in the area.

Nebraska

Jeff Theis, who shot video of a dark funnel cloud near Hardy, Nebraska, said he saw a tornado destroy a farm in the community. Hardy is near the state line with Kansas.

A tornado also hit Roseland, a rural town near Hastings, CNN affiliate WOWT reported.